Alternating-current induction-motor.



u. MCUULLUM. ALTERNATING CURRENT I NDUCTION MOTOR.

Pat ented May 15, 1917.

APPLICATION FILED AUG-2. I915.

2 SHEETS-SHEET 1.

when

B. McCOLLUM.

ALTERNATING CURRENT INDUCTION MOTOR.

\ APPLICATION FILED AUG-2, l9l5;

Patented May'15,1917.

2 SHEETS-SHEET 2.

A&

anon/"00 UNITED STATES PATENT OFFICE. M

BURTON MOCOLLUM, OI WABHINGIION, DISTRICT OF COLUMBIA.

ALTEBNA'IING-GURRENT IN DUCTION-MO'IOB.

To all whom it may (:o'rm'r n Be it known that I, BUR'IQN MoCoLLUM, acitizen of the United States, and a resident of Washington, District ofColumbia, have invented certain new and useful Improvements inAlternating-Current Induction- Motors, of which the following is aspecification.

The object of my invention is to produce an induction motor which willyield a high starting torque with a relatively low starting current, andwhich also will operate under load conditions with good efficiency andsmall speed regulation.

The principle ofumy invention consists broadly in providing a motorhaving two or more magnetic circuits in parallel linking with theprimary winding, one of the magnetic circuits possessing a low magneticreluctance, and the other a relatively high reluctance. My inventionconsists further in providing a'number of secondary electrical. circuitsequal to the number of magnetic circuits, so disposed that one, and oneonly, of said secondary electrical circuits will link with each magneticcircuit. In carrying out my invention it is desirable to provide furtherthat the magnetic circuits of low reluctance shall link with a secondaryelectrical circuit of low resistance, and that the magnetic circuits ofhigh reluctance shall link with secondary electrical circuits ofrelatively high resistance. It will be shown in alater part of thisspecification that a motor so organized will, in general, partake atstarting of the properties of an induction motor having a high secondaryelectrical resistance, while under running conditions it will possesscharacteristics peculiar to a motor having a low secondary resistance.It is well recognized that such properties will accomplish the purposeset forth above as the objectof my invention. All essential details ofmy invention are fully described below,

reference being made to the accompanying drawings.

Ofthe drawings:

Figure 1 is a sectional view of rotor and s'tator'of a motorillustrating the fundamental principle of my invention.

Fig: 2 is a sectional view of a portion of a motor showing one practicalembodiment of my invention.

Figs. 3 and 4 show modified. forms of my invention.

Fig. 5 shows a detail applicable to Fig\ 4.

Specification of Letters Patent. Patented May 15, 191 '1 Applicationfiled August 2, 191'. Serial No. 48,151.

Referring to Fig. 1, 1 is a group of lammations mounted within thestator frame 2. 3 1s a group of laminations mounted on the rotor 4, andplaced within the group 1, and separated therefrom by a very short airgap 5. These two groups of laminations together with the short air gap 5constitute the magnetic circuit of low reluctance referred to above.Near the periphery of the laminations 3 there is laced 1n the usual waya secondary electrical circuit of very low resistance, preferably of thesquirrel cage type as shown at 6. Within the same stator frame 2 isplaced -a second group of laminations 7 beside the group 1, and withinthese and mounted on the shaft 4 is the group of laminations 8, thegroups 7 and 8 being separated by the air gap 9 which is made relativelygreat compared with the air gap 5. The groups of laminations 7 and 8together with the air gap 9 constitute the magnetic circuit of highreluctance referred to above. Near the periphery of the laminations 8 isplaceda secondary electrical winding 10, preferably having a relativelyhigh resistance compared to the winding 6. This Winding is here shown asa squirrel cage winding. 12 and 12 are the short circuiting rings of thesquirrel cage 6, and 13 and 13 of the squirrel cage 10. A primaryelectrical. circuit 11 which may be of any type, is linked with bothmagnetic circuits, the two latter being in parallel as shown.

Considering now the operation of the motor under load conditions and atnear full speed, it will beseen that by far the ater part of themagnetism required to give-the necessary counter electromotive forceint-he primary winding will be carried by the 'laminations 1' and 3 forthe reason that the air gap 9 is so long that the full load currents inthe primary windin can produce relatively little magnetism tierein,while the air gap 5 is made so short that even the resultant of theprimary and secondary magnetizing forces can fproduce the, necessarymagnetism required or the operation'of the motor. It will be apparenttherefore that the motor will operate under the lea-dronditionssubstantially as if the magnetic circuit 7 8, did not exist, and themotor will possess the characteristics afforded by a low winding become;la enough to produce a strong magnetic fi d across the air ga 9. Furter, t e very .low resistance secon ary linking with the magnetic circuit1, 3, will permit a veryheavy current to flow even under a ve smallinducing flux, and this current wil exert a counter magnetizing forcewhich will keep the flux in this magnetic circuit at a small valueduring the starting period. The result will be that during starting andat low speeds most of the flux will link with the high resistanceseconda winding, and the starting characteristics the motor willcorrespond closely'to those of a motor having a large air 'ap and a highsecondary resistance whic conditions, as is well known, tend to 've themotor a high starting torque and ow sta-rtin current.

In genera in carrying out my invention, I prefer that the magnetic core8 be of the smooth core type, the secondary windin or squirrel cage 10being placed on the sur ace 0 thelaminations. Similarly, for the primarycore 7 it is desirable that the teeth be relatively short, or they maybe omitted altogether. This is desirable in order that the air gap 9 mayhave sufiicient magnetic re luctance to cause the motor to operateproperly in accordance with the principles outlined above.

It is important that the construction be such as to keep the reactanceof the electrical circuits as low as possible, and to assist inattaining this end, the short circuiting rings 12 and 13 should be oflarge radialdepth and at the same time the radial de th of thelaminations .in the cores 8 should be as small as possible. This willintroduce a very large reluctance into the magnetic circuit linking withthe rings 12 and 13, thus greatly reducing the reactance and improvingthe operation of the motor.

It was stated above that while the primary electrical circuit should bemade to link with all of the magnetic circuits, the secondary electricalcircults should eac link with one, and one only, of the magneticircuits. This is of great importance for several reasons. In the firstplace, if both the squirrel cages 6 and 10 are interlinked inductivelyby placing them both on a common magnetic core,

the bars of each of the squirrel cages would have to,be placed so farapart that the magnetic leaka of both squirrel cages would be large whicwould be objectionable for reasons well known. In the second place, ifthe squirrel cage 10 were made to link --also-with the core 3 it wouldstill further have its leakage increased .by virtue of its; linking withtwo practically .ir on clad circuits instead of one as here shown, andthe starting characteristics of the motor would be thereby im aired."Still another objection to having the high resistance squirrel cagelink with the core 3 is that it would take up valuable space and make itimpracticable to give the squirrel cage 6 as low a resistance as wouldnerally be desired. It will be seen there ore that it is of greatimportance that each of the secondary electrical windings be linked witha separate and distinct ma etip circuit. I

ile the foregoing description sets forth the fundamental principle of myinvention and the construction shown in Fig. 1 may be used in practice Iprefer in general a modified form, whic however, operates on exactly thesame principle. This modified form is shown in Fig. 2. In thisconstruction there is a main magnetic core 14 mounted in the frame 2,and within the core 14 is a rotor core 15 of the usual type on which isplaced a low resistance windmg 16 preferabl of the squirrel ea c type.Both the secon ary windmg 16 an the primary winding 11 should beembedded in slots in the cores 15 and 14 respectively. These portions ofthe motor, therefore, do not difi'er materially from the usual type. Myinvention consists in part in making use of two additional magneticcircuits in combination with suitable secondary electrical circuitsdescribed below. The two additional magnetic circuits may be derived byplacing over the end connections 17 and 17 of the primary winding 11,rings of magnetic material 18 and 18 laminated this way 'is essentiallysimilar to that clescribed above in reference to Fig. 1. Under ordinaryload conditions when running near full speed, practically all of theflux of the motor will be carried by the main magnetic circuit formedthrough the magnetic cores 14 and 15 and the air gap 5, the reluctanceof the magnetic circuits surrounding the end connections being toohighto permit any considerable amount of magnetism due to the load currents.However, with decreasing speed and increasing currents, the reaction ofthe currents induced in the low resistance squirrel cage 16 greatlyreduces the magnetism in the main magnetic core and causing anincreasing amount of flux to link with the and connections 17 and 17 andthe high resistance secondaries 20 and 20 in inductive relation thereto.This results, as already indicated, in high tongue and relatively smallcurrents at low spec s of the motor.

'Here, as in the case previously described, it is important that thestructure be 'suchthat the reluctance of the magnetic circuits linkingwith the end connecting rings 21 and 22 and 21' and 22' of the secondaryelectrical circuits be'as high as possible, and in order losccure thiscondition these end connecting rings should have a large radial depth,while. the magneticcores 19 and 19 should have the smallest practicableradial depth consistent with adequate cross section to carry the reuired magnetic flux.

if desired, the rings 2land 22 can be replaced by a single ringconnected to both the low resistance squirrel cage 16 and th e highresistance squirrel cage-20, and a slmilar substitution can be made forthe corre sponding rings 21' and 22. This will givegreater economy ofspace and material and permit the currents in each squirrel cage to makea completecircuit without linking with more than one magnetic circuit,which is very important for reasons stated above.

In some cases it would be desirable to simplify the construction byomitting the magnetic cores 18 and 18' over the primary end connection,and alsothe magnetic cores 19 and 19' on the secondaries, thus makingthe two high reluctance magnetic circuits entirely of air spacethroughout. a

It has been stated above that the high resistance secondary windings 20and 20 may be squirrel cage windings, and this would be desirable inmany cases especially if a toothed structure is used for the magneticcores 19 and 19'. When, however, these cores are given a smooth surface,or when they are omitted altogether, the high resistance secondarycircuits may each be made of a solid piece of metal in the form of adrum mounted on each end of the low resistance squirrel cage 16. Oneform of this structure is shown at 23 in Fig. 3 the cores 19 and 19being omitted. This construction has the merit of great simplicity andcheapness. Y

I have found that instead of making the magnetic cores 19 of ordinarymagnetic material such as is generally used in alternating currentapparatus, if these portions be made of a material exhibiting a highhysteresis effect, the starting torque of the motor can be still furtherincreased due to the well known tendency for magnetic material to rotatewith a rotating magnetic field. This tendency to rotate with the fieldis proportional at any given speed to the power loss in the material. Ihave also obtained a very simple, cheap and effective structure by usingsolid steel rings exhibiting this high hysteresis effect for theportions of the magnetic circuit mounted on the secondary mem-' her asshown at 24, Fig. 4. These solid steel rim or drums serve not only asthe carriers of ux and therebydevelop large hysteresis loss withcorresponding torque, but they also serve to a. degree as highresistance secondary electrical circuits owing to the eddy currentsinduced in them by the alternating better conducting material such ascopper,

aluminum or brass. I prefer to make these bands in the form of closedrings which form an integral part of the short clrcuiting rings of theow resistance squirrel cage 16, as shown in Fi 4. The magnetic ring 24should prefer-ab y be beveled on the ed adjoining the main rotor core,as shown in the figure. This reduces the reactance of the squirrel cage.The magnetic rings 24 and 24 may be made of any one of a large number.of magnetically hard alloys. Alloys containing tungsten, chromium ormanganese, or combinations of these metals, with iron as the chiefconstituent are well adapted for use in this connection. I prefer tohave the bands 25 slotted as shown at 26 in Fig. 5 to give substantiallythe same cited; as a squirrel cage construction.

It is preferable in carrying out my invention, to make the endconnections of the primary winding substantially cylindricaLin forminstead of conical, as is most frequently done in the usual types ofmotors. In this Way the mutual inductance between the rimary endconnections and the secon ary electrical circuits is increased and theperformance of the motor correspondingly improved. The cylindrical typeof construction here contemplated is clearly shown in Figs. 1 to 4inclusive.

I have described a structure comprising a single primary electricalcircuit linking with a single magnetic circuit of low resistance andwith a plurality of magnetic circuits of relatively high reluctance. Itwill be evident that there may also be used, if desired,

a plurality of primary electrical circuits and magnetic circuits of lowreluctance, in com- -providing paths of low and substantially unvaryingmagnetic reluctance for the flux -linking said primary winding withcertain of said secondary circuits, and separate paths of high andsubstantially unvarying reluctance for the fluxes linking said pri-'mary winding with the others of said secondary circuits.

2. In aninduction motor, the combinaunvarying magnetic reluctance forthe ,fiux

of relatively h linkin said primary winding with one only of saidsecondar circuits and separate paths of hi h an substantially unvaryingreluctance or the fluxes linking said primary winding with the others ofsaid secondary circuits.

3. In an induction motor, thehaombination of a primary winding, asecondary element providing a plura 1ty of secondary electrical circuitsin inductive relation wit said primary winding, but substantially notinductively related to each other, and means providing paths of low andsubstantially unvarying magnetic reluctance for the flux linking saidprimary winding with certain of said secondar circuits, and separatepaths of hi h an substantially unvarying reluctance or the fluxeslinking said primary winding with the others of said secondary circuits,the said secondary circuits which are linked with the paths of lowreluctance having relatively low electrical resistance, and the saidsecondary circuits linked with the paths of high reluctance havin highresistance.

4. 1 an induction motor, the combination of a primary windin a secondaryelement providing a plur ty of seconda electrical circuits in inductiverelation wit said primary winding, but substantially not inductivelyrelated to each other, and means providing a path of low andsubstantially unvarying magnetic reluctance for the flux linking saidprimary winding with one only of said secondary circuits, and separatepaths of hi h and substantially unvarying reluctance or the fluxeslinking said primary winding with the others of said secondary circults,the said secondary circuit which is linked with the path of lowreluctance, havin a relatively low electrical resistance, an the saidsecondary circuits linked with paths of high magnetic reluctance, havingrelatively high resistance.

5. In an induction motor, the combination of a primary windin with endconnections, and a secondary e ement providing three secondaryelectrical circuits one of said secondary electrical circuits being ininductive relation with the said primary winding through a m eticcircuit of low reluctance, and the 0 or secondary electrical circuitsbeing in inductive, relation with the end11 connfleictionlsi only of thesaid rima win roug magnetic circuits p ry reluctance.

6. In an induction motor, the combination of a primary winding with endconing three secondary electrical cir clude edd nections, and asecondary element providin three secondary electrical circuits, one 0said secondary electrical circuits having a relatively low resistanceand being in inductive relation with the said prima winding through-amagnetic circuit of low reluctan'ce, and the other secondary electricalcircuits having relatively high resistance and being in inductiverelation with the said end connections only of the said primary windingthrough magnetic circuits of relatively high reluctance.

7. In an induction motor, the combination of a primary winding with endconnections, and a secondary element providone of said secondaryelectrical circuits having -a relatively low resistance and-being'ininductive relation with the said prima winding through a magneticcircuit of ow reluctance, and the other secondary electrical circuitshaving relatively high resistance and being in inductive relation withthe said end connections only of the said primary wmdmgjthro h magneticcircuits of relatively gh re uctance, each of said magnetic circuits of'high reluctance consisting in .part of magnetic material mounted on therotor within one of the said high resistance seconda electricalcircuits,

8. an in u ction motor, the combination of a prlmary winding with endconnections,

and a secondary element providing three secondary electrical circuits,one of said secondary electrical circuits having arelatively lowresistance and being in inductive relation with the said primary windingthrou h a magnetic circuit of low reluctance, and t e' one of the saidhigh resistance secondary electrical circuits, and comprising further aring of magnetic material adapted to excurrents surrounding the outersurface 0 one set of end connections of the said primary winding.

9. In an induction motor, the combination of a prima ondary electricalcircuits, one of said secondary electrical circuits having a relativellow resistance and being in inductive relition with the said primarywinding thro h a magnetic circuit of low reluctance, an the othersecondary electrical circuits having relwinding with end connections,

and a secon ary element providing three sec-.

atively high resistance and being in inductive relation with the saidend connections only-of the said primary win through magnetic circuitsof relatively hlgh relucreluctance consistlng in tame, each of saidmagnetic circuits of high art of a ring of magnetic material egrhibitmga high hysteresis a efl'ect mounted on the rotortwithin, one

f the said high resistance secondary elec.-

trical circuits, and comprising further a ring of laminated ma surfaceof one set of end connections of the said primary winding. v

In an induction motor, the combination of a primary winding with endconnections, an three secondary electrical circuits, one of saidsecondary electrical circuits havin a relatively low resistance andbeing in in uctive relation with the said primary winding throu h amagnetic circuit of low reluctance,

and t e other secondary electrical circuits havin relatively highresistance and being in in uctive relation with the said endconnections'only of the saidprimary winding through magnetic circuits ofrelatively high reluctance, said secondary electrical circuits of highresistance comprising metallic cylinders mounted on the rotor at eitherend of the said low resistance secondary electrical circuit and withinthe end connections of the said primary electrical circuit.

11. In an induction motor, the combination of a rimary winding with endconnections, and a secondary element providing three secondaryelectrical circuits, one of" said secondary electrical circuits having arelatively low resistance and being 1ninductive relation with the saidprimary winding through a magnetic circuit of low. reluc-- tance, andthe other secondary electrical circuits'havin relatively high resistanceand being in in uctive relation with the said end connection only of thesaid primary winding through magnetic circuits of relatively highreluctance, said secondary electrical circuits of high resistancecomprising metallic cylinders mounted on the rotor at either end of thesaid low resistance secondary electrical circuit and within the endconnections of the said primary electrical circuit, certain of saidmetallic cylinders being composed of a magnetic material adaptedtopermit eddy currents.

12. In an induction motor, the combination of a primary winding with endconnections, and a secondary element providing three secondaryelectrical circuits, one of said secondary electrical circuits having arelatively low resistance and being in in netive relation with the saidprimary winding throu h a magnetic circuit of low reluctance, and t eother secondary electrical circuits having relatively high resistanceand being in inductive relation with the said end connections only ofthe said primary winding through magnetic circuits of relatively highreluctance, said secondary electrical c1rcu1ts etic' material\exhibitinga low hysteresis e ect surrounding the outer,

a secondary element providing of high resistance comprising metalliccylinders mounted onthe rotor at either endof said metallic cylindersbeing composed of a magnetic material exhibiting a high hystebOSISBfiQOLf m 'a f 13. Inn induction motor, the combination of a primarywinding with end connections, and a secondary element providing threesecondary electrical circuits, one of and secondary electrical circuitshavi a relatively low resistanceand being in in notwo relation with thesaid primary winding throu h a magnetic circuit of low reluctance,

and t e other secondary electrical circuits hav m relatively highresistance and being in in uctlve relation with the said end connectionsonly of the said primary winding through magnetic circuits of relativelyhigh reluctance, said secondary electrical circuits of hlgh resistancecomprising metallic cylinders Inountedon the rotor at either end of thesand low resistance secondary electrical ircult and within the endconnections of the said primary electrical circuit, the said metalliccylinders comprising rings of magnetic material exhibiting a highhysteresis effect, and rings of non-magnetic material 7 surrounding thesaid magnetic rings and in inductive relation with the endconnections ofthe said primary winding.

14. In an induction motor, the combinat1on of a primary windin with endconnections, and a secondary e ement providin three secondary electricalcircuits, one o said secondary electrical circuits having a relativelylow resistance and being in inductive relation with the said primawinding through a magnetic circuit of ow reluctance, and the othersecondary electrical circuits having relatively high resistance andbeing in inductive relation with the said end connections only of the.said primary winding through magnetic circuits of relatively highreluctance, the end connections of the said low resistance secondaryelectrical circuit consisting of rings of good conducting materialadapted to have low reactance.

15. In an induction motor, the combination of a primary winding with endconnections, and a secondary element providing three secondaryelectrical circuits, one of said secondary electrical circuits having arelatively low resistance and being in inductive relation with the saidprimary winding through a magnetic circuit of low reluctance, and theother secondary electrical circuits having relatively hi h resistancewinding tively igh reluctance, each of said magtions,an

netic circuits of high reluctance consisting in part of a ring ofmagnetic material mounted on the rotor within one of the said highresistance secondary electrical circuits, and having a small radialdepth relative to the end connections of the secondary electricalcircuit of low resistance.

16. In'an induction motor, the combination of a rimary winding with endconn'ec-' a secondary element providing three secondary electricalcircuits, one of said secondary electrical circuits having a relativelylow resistance and being in inductive relation with the said primarywinding through tan an circuits having relatively high resistance amagnetic circuit of low relucthe other secondary electrical electricalcircuit of low resistance.

17. In an induction motor, the combination of a primary winding with endconnections, and a secondary element roviding three secondary electricalcircuits, one of said secondary electrical circuits hay in in uctiverelation with the said primary winding through a magnetic circuit of lowreluctance, and the other secondary electrical circuits havingrelatively high resistance and being in inductive relation with the saidend connections only of the said primary winding through magneticcircuits of relatively high reluctance, each of said magnetic circuitsof high reluctance consisting in part of a ring of magnetic materialmounted on the rotor within one of the said high resistance secondaryelectrical circuits,

,a relatively low resistance and being 1n the said highresistancesecondary electrical circuits each comprising a portion of the shortcircuiting ri of the said secondary electrical circuit of ow resistance,the-said portion of said short circuiting rlng being provided with slotsdesignedto make it elec- 4 trically equivalent to what is known as asquirrel cage construction. 7 o

18. In an induction motor, the combination of a primary winding with endconnections, and a secondary element providing three secondaryelectrical circuits, one

of said secondary electrical circuits having a relatively low resistanceand being in inductive relation with the said primary winding through amagnetic circuit of low reluctance, an the other secondary electricalcircuits having relatively high resistance and being in inductiverelation with the said end connections only of the'said primary windingthrough magnetic circuits of relatively high reluctance, each of saidmagnetic circuits of high reluctance consistin in part of magneticmaterial mounted on t e rotor within one of the said high resistancesecondary electrical circuits, the said magnetic material being in theform of a ring with a beveled edge on the side adjoining the main rotorcore adapted to make the radial depth of the said magnetic ring greaternear its outer end than near its inner end.

19. In an induction motor, the combination of a primary winding with endconnections, and a secondary element providin three secondary electricalcircuits, one 0% said secondary electrical circuits being in inductiverelation with the said primary winding throu h a magnetic circuit of lowreluctance, an the other secondary electrical circuits bein in inductiverelation with the end connections only of the said primary windinthrough magnetic-circuits of relatively hig reluctance; the said endconnections of the primary electrical circuit having collectively,substantially a cylindrical form.

BURTON MOCOLLUM.

